One problem with quartz sound references in the tuning exam is that they produce a perfect 3rd harmonic that beats with the 3rd partial of the piano string when the fundamentals are beatless. You can train yourself to ignore the 3rd parial and listen only to the fundamental, but that is an extra effort that is not necessary when using a tuning fork. Tuning forks are very good at producing only the fundamental. Bill Bremmer researched this a while ago to determine why users of the Sanderson Accufork were often tuning the A440 too low in the exam.
Robert Scott
Ypsilanti, Michigan
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